Cytokines play important roles in the regulation of hematopoiesis and immune responses, and can influence lymphocyte development. The human class II cytokine family includes interferon-α (IFN-α) subtypes, interferon-β (IFN-β), interferon-γ (IFN-γ), IL-10, IL-19 (U.S. Pat. No. 5,985,614), MDA-7 (Jiang et al., Oncogene 11, 2477-2486, (1995)), IL-20 (Jiang et al., Oncogene 11, 2477-2486, (1995)), IL-22 (Xie et al., J. Biol. Chem. 275, 31335-31339, (2000)), and AK-155 (Knappe et al., J. Virol. 74, 3881-3887, (2000)). Most cytokines bind and transduce signals through either Class I or Class II cytokine receptors. Members of human class II cytokine receptor family include interferon-αR1 (IFN-αR1), interferon-γ-R2 (IFN-γ-R2), interferon-γR1 (IFN-γR1), interferon-γR2 (IFN-γR2), IL-10R (Liu et al., J. Immunol. 152, 1821-1829, (1994)), CRF2-4 (Lutfalla et al. Genomics 16, 366-373, (1993)), IL-20Rβ (Blumberg et al., Cell 104, 9-19, (2001)) (also known as zcytor7 (U.S. Pat. No. 5,945,511) and CRF2-8 (Kotenko et al., Oncogene 19, 2557-2565, (2000)), IL-20Rβ (Blumberg et al., ibid, (2001)) (also known as DIRS1 (PCT WO 99/46379)), IL-22RA1 (IL-22 receptor-α1, submitted to HUGO for approval) (also known as IL-22R (Xie et al., J. Biol. Chem. 275, 31335-31339, (2000)), zcytor11 (U.S. Pat. No. 5,965,704) and CRF2-9 (Kotenko et al., Oncogene 19, 2557-2565, (2000)), and tissue factor.
Class II cytokine receptors are typically heterodimers composed of two distinct receptor chains, the α and β receptor subunits (Stahl et al., Cell 74, 587-590, (1993)). In general, the α subunits are the primary cytokine binding proteins, and the β subunits are required for formation of high affinity binding sites, as well as for signal transduction. An exception is the IL-20 receptor in which both subunits are required for IL-20 binding (Blumberg et al., ibid, (2001)).
The class II cytokine receptors are identified by a conserved cytokine-binding domain of about 200 amino acids (D200) in the extracellular portion of the receptor. This cytokine-binding domain is comprised of two fibronectin type III (FnIII) domains of approximately 100 amino acids each (Bazan J. F. Proc. Natl. Acad. Sci. USA 87, 6934-6938, (1990); Thoreau et al., FEBS Lett. 282, 16-31, (1991)). Each FnIII domain contains conserved Cys, Pro, and Trp residues that determine a characteristic folding pattern of seven, β-strands similar to the constant domain of immunoglobulins (Uze et al., J. Interferon Cytokine Res. 15, 3-26, (1995)). The conserved structural elements of the class II cytokine receptor family make it possible to identify new members of this family on the basis of primary amino acid sequence homology.
The interleukins are a family of cytokines that mediate immunological responses, including inflammation. Central to an immune response is the T cell, which produce many cytokines and adaptive immunity to antigens. Cytokines produced by the T cell have been classified as type 1 and type 2 (Kelso, A. Immun. Cell Biol. 76:300-317, 1998). Type 1 cytokines include IL-2, interferon-gamma (IFN-γ), LT-α, and are involved in inflammatory responses, viral immunity, intracellular parasite immunity and allograft rejection. Type 2 cytokines include IL-4, IL-5, IL-6, IL-10 and IL-13, and are involved in humoral responses, helminth immunity and allergic response. Shared cytokines between Type 1 and 2 include IL-3, GM-CSF and TNF-α. There is some evidence to suggest that Type 1 and Type 2 producing T cell populations preferentially migrate into different types of inflamed tissue.
Of particular interest, from a therapeutic standpoint, are the interferons (reviews on interferons are provided by De Maeyer and De Maeyer-Guignard, “Interferons,” in The Cytokine Handbook, 3rd Edition, Thompson (ed.), pages 491-516 (Academic Press Ltd. 1998), and by Walsh, Biopharmaceuticals: Biochemistry and Biotechnology, pages 158-188 (John Wiley & Sons 1998)). Interferons exhibit a variety of biological activities, and are useful for the treatment of certain autoimmune diseases, particular cancers, and the enhancement of the immune response against infectious agents, including viruses, bacteria, fungi, and protozoa. To date, six forms of interferon have been identified, which have been classified into two major groups. The so-called “type I” IFNs include IFN-α, IFN-β, IFN-ω, IFN-δ, and interferon-τ. Currently, IFN-γ and one subclass of IFN-α are the only type II IFNs.
Type I IFNs, which are thought to be derived from the same ancestral gene, have retained sufficient similar structure to act by the same cell surface receptor. The α-chain of the human IFN-α/β receptor comprises an extracellular N-terminal domain, which has the characteristics of a class II cytokine receptor. IFN-γ does not share significant homology with the type I IFN or with the type II IFN-α subtype, but shares a number of biological activities with the type I IFN.
Clinicians are taking advantage of the multiple activities of interferons by using the proteins to treat a wide range of conditions. For example, one form of IFN-α has been approved for use in more than 50 countries for the treatment of medical conditions such as hairy cell leukemia, renal cell carcinoma, basal cell carcinoma, malignant melanoma, AIDS-related Kaposi's sarcoma, multiple myeloma, chronic myelogenous leukemia, non-Hodgkin's lymphoma, laryngeal papillomatosis, mycosis fungoides, condyloma acuminata, chronic hepatitis B, hepatitis C, chronic hepatitis D, and chronic non-A, non-B/C hepatitis. The U.S. Food and Drug Administration has approved the use of IFN-β to treat multiple sclerosis, a chronic disease of the nervous system. IFN-γ is used to treat chronic granulomatous diseases, in which the interferon enhances the patient's immune response to destroy infectious bacterial, fungal, and protozoal pathogens. Clinical studies also indicate that IFN-γ may be useful in the treatment of AIDS, leishmaniasis, and lepromatous leprosy.
IL-28A, IL-28B, and IL-29 comprise a recently discovered new family of proteins that have sequence homology to type I interferons and genomic homology to IL-10. This new family is fully described in co-owned PCT application WO 02/086087 and Sheppard et al., Nature Immunol. 4:63-68, 2003; both incorporated by reference herein. Functionally, IL-28 and IL-29 resemble type I INFs in their ability to induce an antiviral state in cells but, unlike type I IFNs, they do not display antiproliferative activity against certain B cell lines.
IL-28 and IL-29 are known to have an odd number of cysteines (PCT application WO 02/086087 and Sheppard et al., supra.) Expression of recombinant IL-28 and IL-29 can result in a heterogeneous mixture of proteins composed of intramolecular disulfide bonding in multiple conformations. The separation of these forms can be difficult and laborious. It is therefore desirable to provide IL-28 and IL-29 molecules having a single intramolecular disulfide bonding pattern upon expression and methods for refolding and purifying these preparations to maintain homogeneity. Thus, the present invention provides for compositions and methods to produce homogeneous preparations of IL-28 and IL-29.